Multiple flash unit with light-spreading protective shield

Abstract

A prismatic protective shield for each flash-lamp and reflector combinationas arrays of parallel prisms in order to level the light distribution with a tendency to produce an intensity dip at the pattern center. Arrays of horizontal prisms occupy a central vertical stripe of the shield plane. Arrays of vertical prisms are at each side of the horizontal prisms.

We claim: 
     
       1. A multiple flash unit suitable for instantdevelopment photography by direct flash illumination, comprising a plurality of combustion-type flash lamps each provided with a reflector and all held on a carrier capable of being mounted on a camera, in which unit the improvement is incorporated which consists in that: a protective transparent shield of prismatically varying thickness having arrays of light-spreading oblique refraction surfaces is provided in front of each lamp-and-reflector combination for producing, in combination with the reflector of the lamp-and-reflector combination, a light distribution over a picture-taking pyramidal angle of view which is less in the central direction and increases, at least in the mid-portion of said pyramidal angle, as the angle of radiation deviates from the central direction towards the boundaries of said angle of view.   
     
     
       2. A multiple flash unit as defined in claim 1, in which said arrays of light-spreading oblique refraction surfaces of said protective shield are arrays of juxtaposed parallel prisms at least one pair of said arrays having their directions of parallelism respectively in each of two mutually perpendicular directions. 
     
     
       3. A multiple flash unit as defined in claim 2, in which at least one of said parallel prism arrays have an array of normally horizontally disposed prisms and at least one of said parallel prism arrays is an array of normally vertically disposed prisms. 
     
     
       4. A multiple flash unit as defined in claim 2, in which said parallel prism arrays consist of two arrays of horizontal prisms disposed one above the other and together occupying a central vertical stripe of said protective shield and two of said parallel prism arrays are arrays of vertical prisms, each at one side of said vertical stripe occupied by said arrays of horizontal prisms with all prisms having a light-spreading configuration. 
     
     
       5. A multiple flash unit as defined in claim 4, in which said pair of arrays of horizontal prisms and also said pair of arrays of vertical prisms are disposed symmetrically with respect to the center of the protective shield provided in front of an individual lamp-and-reflector combination. 
     
     
       6. A multiple flash unit as defined in claim 5 in which said arrays of horizontal prisms have refractive surfaces at a refractive angle (α) of about 36° and a ridge angle of about 64° and said arrays of verticle prisms have refractive surfaces at a refractive angle (β) of about 20° and a ridge angle (δ) of about 90°. 
     
     
       7. A multiple flash unit as defined in claim 5 in which the ratio of the width of said central vertical stripe to the width of each array of vertical prisms is approximately to 7:6.